FORTUNE — Today, for the first time, more people worldwide live in cities than in the countryside. What’s often missed in this equation is how fast this trend will accelerate. Take China. Currently 650 million people, or 52% of the population, now live in cities. Fast-forward only 10 years or so, and that number is expected to hit one billion. That means that some 350 million people, the equivalent of the entire population of the U.S., will move from the Chinese countryside into urban areas. The number of Chinese cities with a million or more people will hit 221.
This migration presents a challenge. China’s urban dwellers on average consume three times more energy than rural ones. That means we must design new cities and rebuild old ones in ways that will allow billions to live, drive, eat, and work sustainably. At today’s session on Rethinking Our Cities at Fortune Global Forum in Chengdu, Zhang Yue, the CEO of Broad Group, a maker of energy equipment and a real estate development company, said that we have to totally redefine what it means to live in cities.
“People don’t want to have to get on trains or drive a car to get to work,” he said. One solution: Zhang plans to lick the urban congestion problem by building up. His proposed high-rise prefab in Hunan Province called Sky City will soar 202 stories to a height of 838 meters.
MORE: Complete coverage of the Fortune Global Forum
Zhang says that Sky City can be built in seven months compared to at least five years for other super high-rises and is five times more energy efficient. The building will save some 200 hectares compared to typical sprawl development in China and will contain offices, schools, playing fields, stores and restaurants, reducing dependency on the automobile. Says Zhang: “Sky City will take some 2,000 cars off the road simply because its residents can find most of what they need right where they live.”
Another proponent of smart cities is Jean-Pascal Tricoire, the CEO of Schneider Electric, the French company that offers solutions for power, grids, traffic systems, and more. Tricoire says cities can embrace social media to make them run more sustainably. “Parisians,” he says, “spend a year of their lives looking for parking spaces.” He says his company is working on systems where drivers can tap into social media and find an empty parking spot or avoid traffic jams.
David Cote, the CEO of Honeywell (HON), the industrial giant that has more than 50% of its portfolio linked to energy efficiency, gave a telling example of how the city of the future will require dramatically less energy. The company has designed building management systems that integrate core systems such as HVAC, lighting, and security that maximize energy usage while providing cost savings.
MORE: China’s big bet on transportation
So the world has recognized the challenge of making our cities more sustainable and has the technology to do it. Cote says that’s not enough. “We can’t let this process be chaotic. We need much more planning. We need to get a lot of smart people in a room to figure out how to make all this work.”
The three executives on this panel would certainly be well-suited to lead the discussion.
